Nanowires of indium phosphide grown directly on an electrode greatly increase the flow of electrons through a polymer film to the electrode. Although still at the proof of concept stage, this nanotech innovation could ultimately lead to more efficient thin-film solar cells. Excerpts from a University of California, San Diego news release, by Daniel Kane “Nanowires May Boost Solar Cell Efficiency, UC San Diego Engineers Say” (credit PhysOrg.com)

University of California, San Diego electrical engineers have created experimental solar cells spiked with nanowires that could lead to highly efficient thin-film solar cells of the future.

Indium phosphide (InP) nanowires can serve as electron superhighways that carry electrons kicked loose by photons of light directly to the device’s electron-attracting electrode — and this scenario could boost thin-film solar cell efficiency, according to research recently published in Nano Letters (paper).

The new design increases the number of electrons that make it from the light-absorbing polymer to an electrode. By reducing electron-hole recombination, the UC San Diego engineers have demonstrated a way to increases the efficiency with which sunlight can be converted to electricity in thin-film photovoltaics.

Including nanowires in the experimental solar cell increased the “forward bias current” — which is a measure of electrical current — by six to seven orders of magnitude as compared to their polymer-only control device, the engineers found.

…The researchers say they were the first group to publish work demonstrating growth of nanowires directly on metal electrodes without using specially prepared substrates such as gold nanodrops.

“Just a layer of metal can work. In this paper we used ITO [indium tin oxide], but you can use other metals, including aluminum,” said [co-author] Paul Yu.

Growing nanowires directly on untreated electrodes is an important step toward the goal of growing nanowires on cheap metal substrates that could serve as foundations for next-generation photovoltaics that conform to the curved surfaces like rooftops, cars or other supporting structures, the engineers say.

“By growing nanowires directly on an untreated electrode surface, you can start thinking about incorporating millions or billions of nanowires in a single device. I think this is where the field is eventually going to end up,” said [first author Clint] Novotny. “But I think we are at least a decade away from this becoming a mainstream technology.”